Hi, as we all know. when we are doing dimension. the center of the cross (cursor) suppose to have a small square and this small square will have us to point the edge of the object . so that we can do the dimensioning much more easy and accurately. but i don't know why mine small little square disappear. can someone help ?  

Object snap is probably turned off, F3 to make it on/offuploads/404719/Capture.zipright-click on the icon to see/turn (on/off) some snaps

But even if F3 Object Snaps are on, if the ones you want aren't selected you still might not be able to select points to dimension from.  So to be sure, type OBJECTSNAP (or OSNAP) at the command line and double check that the running snap settings are the ones you want.Dave.